Objective: The experience of pain is believed to be influenced by psychologic and genetic factors. A previous study suggested pain catastrophizing and catechol-O-methyltransferase (COMT) genotype influenced clinical pain ratings for patients seeking operative treatment of shoulder pain. This study investigated whether these same psychologic and genetic factors predicted responses to induced shoulder pain.
Methods: Participants (n=63) completed self-report questionnaires and had COMT genotype determined before performing a standardized fatigue protocol to induce delayed onset muscle soreness. Then, shoulder pain ratings, self-report of upper-extremity disability ratings, and muscle torque production were reassessed 24, 48, and 72 hours later.
Results: This cohort consisted of 35 women and 28 men, with a mean age of 20.9 years (SD=1.7). The frequency of COMT diplotypes was 42 with “high COMT enzyme activity” (low pain sensitivity group) and 21 with “low COMT enzyme activity” (average pain sensitivity/high pain sensitivity group). A hierarchical regression model indicated that an interaction between pain catastrophizing and COMT diplotype was the strongest unique predictor of 72-hour pain ratings. The same interaction was not predictive of self-report of disability or muscle torque production at 72 hours. The pain catastrophizing×COMT diplotype interaction indicated that participants with high pain catastrophizing and low COMT enzyme activity (average pain sensitivity/high pain sensitivity group) were more likely (relative risk=3.5, P=0.025) to have elevated pain intensity ratings (40/100 or higher).
Discussion: These findings from an experimental model converge with those from a surgical cohort and provide additional evidence that the presence of elevated pain catastrophizing and COMT diplotype indicative of low COMT enzyme activity have the potential to increase the risk of developing chronic pain syndromes.
*Department of Physical Therapy, Brooks Center for Rehabilitation Studies
†Department of Applied Physiology and Kinesiology
‡Department of Molecular Genetics and Microbiology, Center for Mammalian Genetics
∥Department of Community Dentistry and Behavioral Science, University of Florida, Gainesville FL
§Department of Physical Medicine and Rehabilitation, Health Ministry, Ankara Diskapi, Education and Research Hospital, Hosdere Caddesi, Ankara, Turkey
Funded by the University of Florida, Research Opportunity Incentive Fund, no. 56577 (S.Z.G.) and by NS41670 (R.B.F.).
Reprints: Steven Z. George, PT, PhD, Department of Physical Therapy, Brooks Center for Rehabilitation Studies, University of Florida, Health Science Center, PO Box 100154, Gainesville, FL 32610-0154 (e-mail: firstname.lastname@example.org).
Received for publication December 14, 2007; revised April 1, 2008; accepted April 13, 2008